1. Technical Field
The present invention relates to light fixtures, and more particularly to light emitting diode fixtures configured for easy maintenance and efficient use for retrofit in or replacement of fluorescent lights or fixtures.
2. Description of the Related Art
Existing linear fluorescent lighting fixtures utilize tube lamping in conjunction with a ballast and reflector to provide a lighting solution. Omnidirectional light output from a linear fluorescent light source is either directly or indirectly projected from the fixture in conjunction with some form of reflecting system or lens. Typical fluorescent tubes are terminated with either a single pin or multiple pins which are fit into sockets which are wired to a ballast.
Typical useful life of fluorescent tube lamps is limited to 15,000 hours. Poor connections at the junction point of the lamp and socket results in premature lamp failure as well as a potential fire hazard due to arcing. Older magnetic ballasts contain hazardous PCBs and pose a disposal problem when replaced with newer solid state ballasts. Common fluorescent light fixtures are not dimmable and perform poorly in cold temperature applications when not jacketed.
Fluorescent light tubes contain mercury and must be discarded using an environmentally sound method. Battery backed up fluorescent emergency lighting is complex (e.g., inverter type ballasts are required), is costly and provides a very limited operating time due to the high wattage needed. Fluorescent tubes are manufactured in various lengths and styles (T5, T8, T12, etc.), which provide a common average of 50-67 lumens per watt when powered with modern electronic ballasts.
A possible replacement/retrofit for linear fluorescent fixtures is to re-lamp a fluorescent fixture with LED tube lamps. LED tubes are self-contained light engines consisting of LED light sources, a solid state driver, thermal management and lensing. These tubes are designed to fit the form factor of existing fluorescent tube styles and sizes (i.e., T5, T8, T12, etc.). LED tubes do not accept the voltage output of the existing fluorescent ballast. The tubes require the fixture to be re-wired, typically bypassing the ballast and supplying the retrofit tube with the mains voltage.
Due to limitations in their construction LED tubes have a limited light projection angle which under-utilizes the existing reflector and creates a narrower and distorted light distribution profile with shadows and hot spots. Heat from the LEDs is trapped in the sealed tube and is typically dissipated by an aluminum heat-sink on the top side of the tube itself. The limited heat dissipation of the tube heat sink typically shortens the product life of the LEDs and the encapsulated driver electronics. The wattage of the LED tube is practically limited by the ability to dissipate heat from the encapsulated light engine. The constant current/voltage integral driver encapsulated within the LED tube does not provide any means for dimming the light output. The reliability of the system is based on the socket to tube connection which is subject to contamination and vibration. Emergency battery backup operation is once again complex, costly and provides a very limited operating time due to the high wattage of the entire tube system.